The chemicals which are "pro-life" with reference to human beings

Options

A. Are regarded as one of the most significant discovery of twenty first century
B. Have rarely contributed to human welfare
C. Are produced by some plants and all animals
D. Can kill or retard the growth of disease-causing microbes

Answer

### Step-by-Step Solution:

1. **Understanding Pro-life Chemicals**:
- Pro-life chemicals refer to substances that promote life by inhibiting or killing pathogens, which are microorganisms that cause diseases.

2. **Identifying Characteristics of Pro-life Chemicals**:
- These chemicals have two main characteristics:
- They can stop the growth of pathogens.
- They can kill pathogens.

3. **Evaluating the Options**:
- The question provides multiple options regarding the characteristics of pro-life chemicals. We need to evaluate each option based on the definition of pro-life chemicals.

4. **Analyzing Each Option**:
- **Option 1**: "Regarded as one of the most significant discoveries of the 21st century."
- This is incorrect because while pro-life chemicals are important, this statement does not accurately describe their function.

- **Option 2**: "Have rarely contributed to human welfare."
- This is also incorrect as pro-life chemicals significantly contribute to human health and welfare by controlling diseases.

- **Option 3**: "Are produced by some plants and all animals."
- This statement is incorrect because not all animals produce pro-life chemicals, and the statement is too broad.

- **Option 4**: "Can kill or retard the growth of disease-causing microorganisms."
- This is the correct option as it accurately describes the function of pro-life chemicals.

5. **Conclusion**:
- The correct answer is that pro-life chemicals can kill or retard the growth of disease-causing microorganisms.